The fertilization of animals by artificial insemination (AI) and embryo transplant following in vitro fertilization is an established practice. In the livestock production industry, the ability to influence the reproductive outcome toward offspring having one or more desired characteristics has obvious advantages. By way of example, there would be an economic benefit in the dairy industry to preselect offspring in favor of the female sex to ensure the production of dairy cows. The separation of sperm into enriched populations of X and Y chromosome-bearing cells, known as gender enriched semen or gender enriched sperm, is one method of achieving preselected offspring.
In order to obtain gender enriched semen, sperm cells must be stained with a dye and subsequently sorted into X and Y chromosome-bearing cells. Each of staining and sorting processes places a stress on the sperm cells that decreases sperm cell viability or motility, particularly progressive motility. Especially stressful is the process of staining the sperm cells, which requires contacting the cells at with a dye for a certain period of time, often at a temperature and pH which are not common in the typical sperm cell environment.